The invention relates generally to the field of small particle formation and more specifically to fields where (1) it is important to create solid particles, liquid particles or gas bubbles which are very small and uniform in size and/or (2) it is important to avoid nozzle clogging when small nozzle openings are used to expel a fluid over a long period of time.
Monodispersed sprays of droplets of micrometric size have attracted the interest of scientist and engineers because of their potential applications in many fields of science and technology. Recently, the possibility of getting medicines into patients via pulmonary inhalation is being actively investigated by pharmaceutical companies around the world R. F. Service (1997), xe2x80x9cDrug Delivery Takes a Deep Breath,xe2x80x9d Science 277:1199-1200. Classifying a polydispersed aerosol (for example, by using a differential mobility analyzer, B. Y. Liu et al. (1974), xe2x80x9cA Submicron Standard and the Primary Absolute Calibration of the Condensation Nuclei Counter,xe2x80x9d J. Coloid Interface Sci. 47:155-171 or breakup process of Rayleigh""s type of a capillary microjet Lord Rayleigh (1879), xe2x80x9cOn the instability of Jets,xe2x80x9d Proc. London Math. Soc. 10:4-13, are the current methods to produce the monodispersed aerosols of micrometric droplets needed for such applications. The substantial loss of the aerosol sample during the classification process can severely limit the use of this technique for some applications. On the other hand, although in the capillary break up the size distribution of the droplets can be very narrow, the diameter of the droplets is determined by the jet diameter (approximately twice the jet diameter). Therefore, the generation and control of capillary microjets are essential to the production of sprays of micrometric droplets with very narrow size distribution.
Capillary microjets with diameters ranging from tens of nanometers to hundred of micrometers are successfully generated by employing high electrical fields (several kV) to form the well-known cone-jet electrospray. Theoretical and experimental results and numerical calculations on electrosprays can be obtained from M. Cloupean et al. (1989), xe2x80x9cElectrostatic Spraying of Liquids in Cone Jet Mode,xe2x80x9d J. Electrostat 22:135-159, Fernxc3xa1ndez de la Mora et al. (1994), xe2x80x9cThe Current Transmitted through an Electrified Conical Meniscus,xe2x80x9d J. Fluid Mech. 260:155-184 and Loscertales (1994), A. M. Gaxc3x1xc3xa1n-Calvo et al. (1997), xe2x80x9cCurrent and Droplet Size in the Electrospraying of Liquids: Scaling Laws,xe2x80x9d J. Aerosol Sci. 28:249-275, Hartman et al. (1997), xe2x80x9cElectrohydrodynamic Atomization in the Cone-Jet Mode,xe2x80x9d Paper presented at the ESF Workshop on Electrospray, Sevilla, Feb.28-Mar. 1, 1997 among others [see also the papers contained in the Special Issue for Electrosprays (1994)]. In the electrospray technique the liquid to be atomized is slowly injected through a capillary electrified needle. For a certain range of values of the applied voltage and flow rate an almost conical meniscus is formed at the needle""s exit from whose vertex a very thin, charged jet is issued. The jet breaks up into a fine aerosol of high charged droplets characterized by a very narrow droplet size distribution. Alternatively, the use of purely mechanical means to produce capillary microjets is limited in most of applications for several reasons: the high-pressure values required to inject a liquid through a very narrow tube (typical diameters of the order of few micrometers) and the easy clogging of such narrow tubes due to impurities in the liquid.
The present invention provides a new technique for generating steady microcapillary jets exclusively based on mechanical means which does not present the above inconveniences and can compete advantageously with electrospray atomizers. The jet diameters produced with this technique can be easily controlled and range from below one micrometer to several tens of micrometers.
Spherical particles of liquid in the form of a monodispersion as well as spherical particles of bubbles in the form of a monodispersion are disclosed wherein the particles have a size on the order of 0.1 to 100 microns. The particles are created by various types of systems and devices disclosed herein. The device includes a primary source of a stream of liquid or gas which is forced through, respectively, a gas or liquid held under pressure in a pressure chamber. The pressure chamber has an exit opening through which the stream is allowed to flow surrounded by the surrounding gas or liquid. As the stream flows toward the exit opening it forms a stable capillary microjet which jet disassociates upon exiting the chamber: When certain parameters are correctly chosen the particles or bubbles formed are all substantially uniform in size with a very small degree of deviation, e.g., xc2x13% to xc2x110%. The particles and bubbles are produced using a relatively small amount of energy compared with the amount of energy used to produce such in comparable systems. Small particles of liquid may be used in a variety of applications including fuel injection engines and the production of aerosols for the delivery of drugs by inhalation. Small bubbles may be used for a variety of uses including decontamination of gases and oxygenation of sewage or water in which fish or other plant or animal life is present and in need of oxygen.